Reaction-sintered silicon carbide (RS-SiC) has been widely used in the industrial fields for its excellent physical and chemical properties. Oxidation-assisted polishing is an important machining method for obtaining SiC parts with high precision. Through plasma oxidation, thermal oxidation, and anodic oxidation, soft oxide can be obtained on the RS-SiC substrate. With the assistance of abrasive polishing to remove the oxide rapidly, the material removal rate can be increased and the surface quality can be improved. The experimental results indicate that the surface roughness root-mean-square (rms) and roughness-average (Ra) can reach 0.626nm and 0.480nm by plasma oxidation-assisted polishing; in thermal oxidation-assisted polishing, the rms and Ra can be 0.920nm and 0.726nm; in anodic oxidation, the calculated oxidation rate is 5.3nm/s based on Deal-Grove model, and the rms and Ra is 4.428nm and 3.453nm in anodic oxidation-assisted polishing. The oxidation-assisted polishing can be propitious to improve the process level in machining RS-SiC, which would promote the application of SiC parts in optics and ceramics fields.